The beneficiary regard public pension fund as risk free asset. It is reason why the government guarantee the pension members pension benefit with no relation of fund investment result. But the pension members predict changing of pension scheme when the pension liability exceed pension asset plus government pension support ability. When pension liability is bigger than government payment due to poor pension fund performance, the members think that pension scheme must be changed. They consider that pension contribution rate will be raised or beneficiary will be reduced. They regard pension benefit right as risk asset including possibility of changing in consequence of pension fund result. In this paper, I try to estimate discount rate of pension liability including pension scheme risk; the probability of reducing beneficiary or raising contribution.